As is generally known, the measurement of magnetic fields of a low intensity such as, for example, the earth's magnetic field, is possible with sensors utilizing an anisotropic magnetoresistive effect. But when large temperature changes occur, considerable problems arise because of a quite significant zero drift, in spite of a sufficient magnetic field sensitivity.
One method for the eliminating zero drift for magnetoresistive sensor bridges is described in the Technical Information 901 228 of Philips Components. The magnetoresistive sensor bridge is placed in a wound coil. Short current pulses of alternating direction through the coil generate a sufficient magnetic field to set the self-magnetization of the magnetoresistive film strips in the corresponding direction. Since the sensor signal changes its polarity with the reversal of the magnetization direction, the drift of the sensor bridge is also eliminated when the magnetic-field-proportional alternating component is separated from the steady component, which contains the zero voltage of the sensor bridge. But the production of such coils is expensive. Their inductance limits the measuring frequency. Adjusting the sensor elements in the coil is an expensive step, in particular when all three magnetic field components in the space are to be measured with an arrangement.